(a) Schematic of human lung structure showing an enlarged view of an alveolar-capillary barrier (ACB) in a pulmonary alveolus. Apical side of the epithelium cell sheet (ECS) lying on a basement membrane (BM) is covered with a thin lung liquid lining (LLL) layer and forms an air-liquid interface (ALI). Instabilities at the ALI can create a liquid plug (LP) that occludes small airways. The basal side of the barrier is made of an interstitium (Int) and capillaries (Cp) in close juxtaposition with the BM. Capillaries possess an inner lining of endothelial cells (ECs) and red blood cells (RBCs) flow through these vessels. The interstitium contains connective tissue fibers (CTFs) and other various types of cells. (b) Application of microfluidic technology across four major areas of respiratory physiology. The simplest microfluidic device is generally fabricated by sealing a poly(dimethylsiloxane) (PDMS) mold against a flat substrate (e.g., glass and PDMS).
